potential re change for 5.3?

[Scott Long]

Poul-Henning Kamp wrote:
> In message <412D0868.9060203 at freebsd.org>, Scott Long writes:
> 
> 
>>I'm not suggesting anything different, just making a note of something
>>that might be desirable in the future.  In a way, I see GEOM as having
>>the potential to be like Netgraph where it intercepts operations that it
>>wants to process through it's framework and lets ones that it doesn't 
>>pass directly through without a decoupling through extra kernel threads.
>>But that's only one possible strategy.  Introducing the concept of a
>>I/O scheduler that spawns KSE's to handle individual I/O requests is
>>another possibility.
> 
> 
> Well, the problem here is that requests which cannot be dealt with
> due to resource shortages should be queued at the level where they
> require least resources.  A request queued inside a driver holds
> far more resources than a request in the pure bio format at the
> entrance to the driver for instance.

Not necessarily.  It's not hard for a driver to keep a request queued on
the bioq and not consume and driver resources at all.

> 
> And spawning KSE's in low memory situations is a recipe for suicide.
> 

Probably true.

Scott